Inactivation modeling of human enteric virus surrogates, MS2, Qβ, and ΦX174, in water using UVC-LEDs, a novel disinfecting system

Unveiling the inactivation mechanisms of different viruses in sludge anaerobic digestion based on factors identification and damage analysis

Despite anaerobic digestion having potential for pathogen reduction in sewage sludge, the behaviors of viruses as the primary health concern are rarely studied. This study investigated the inactivation kinetics and mechanisms of four typical virus surrogates with different structures in mesophilic (MAD) and thermophilic (TAD) anaerobic digestion of sludge. Virus inactivation in MAD was virus-type-dependent correspondingly to different function loss. Temperature drove the faster inactivation proceeding for enveloped Phi6, while temperature and ammonia were the critical inactivation factors for nonenveloped MS2, causing genome degradation and protein functional damage. Interaction with sludge solids played critical role in DNA viruses T4 and Phix174 inactivation via inducing host binding function damage. By comparison, TAD enhanced viral protein denaturation, bringing efficient inactivation with reducing heterogeneity among nonenveloped viruses. These insights into unique virus behaviors in anaerobic digestion systems can provide guidance for developing more effective disinfection protocols and improving sludge biosafety.

Efficacy of UVC-LED radiation in bacterial, viral, and protozoan inactivation: an assessment of the influence of exposure doses and water quality

Ultraviolet light-emitting diodes (UV-LEDs) have demonstrated the ability to inactivate microorganisms in water, offering an environmentally safer alternative to the conventional mercury lamp, in UV applications. While several studies have explored the microbiological effect of UVC-LEDs (200nm-280nm), limited information exists regarding their effects on waters with critical qualities. These critical qualities encompass bacteria, viruses, and protozoa - drinking water quality indicators defined by the World Health Organization for small water systems. For the first time, this work reports on the Escherichia coli, PhiX-174, MS2, and Cryptosporidium oocysts inactivation using a bench-scale UVC-LED (280 nm) water disinfection system. UV doses at a wavelength of 280 nm (UV280) of up to 143.4 mJ/cm2 were delivered under two quality-critical water conditions: filtered water (UV transmittance at 280 nm - UVT280 90.2 %) and WHO challenge water (UVT 15.7 %). Results revealed microbiological reductions dependent on exposure time and UVT. For UV280 dose of 16.1 mJ/cm2, 2.93-3.70 log E. coli reductions were observed in UVT 90.2 % and 15.7 %, 3.49-4.21 log for PhiX-174, 0.63-0.78 log for MS2, and 0.02-0.04 log for Cryptosporidium oocysts. Significantly higher UV280 doses of 143.4 mJ/cm2 led to reductions of 3.94-5.35 log for MS2 and 0.42-0.46 log for Cryptosporidium oocysts. Statistical analysis revealed that the sensitivity among the organisms to UV280 exposure was E. coli = PhiX-174 > MS2 >> Cryptosporidium oocysts. Although experiments with WHO challenge water posed greater challenges for achieving 1 log reduction compared to filtered water, this difference only proved statistically significant for PhiX-174 and MS2 reductions. Overall, UVC-LED technology demonstrated notable efficacy in microbiological inactivation, achieving significant reductions based on WHO scheme of evaluation for POU technologies in both bacteria and viruses even in critical-quality waters. The findings emphasize the potential for extending the application of UVC-LED as a viable solution for household water treatment.

Visible-light photoactivated proanthocyanidin and kappa-carrageenan coating with anti-adhesive properties against clinically relevant bacteria

The increase of bacterial resistance to antibiotics is a growing concern worldwide and the search for new therapies could cost billions of dollars and countless lives. Inert surfaces are major sources of contamination due to easier adhesion and formation of bacterial biofilms, hindering the disinfection process. Therefore, the objective of this study was to develop a photoactivatable and anti-adhesive kappa-carrageenan coating using proanthocyanidin as a photosensitizer. The complete reduction (>5-log10 CFU/cm3) of culturable cells of Staphylococcus aureus, Escherichia coli and Pseudomonas aeruginosa pathogens was achieved after 30 min of exposure to visible light (420 nm; 30 mW/cm2) with 5 % (w/v) of the photosensitizer. Cell membrane damage was confirmed by measuring potassium leakage, epifluorescence microscopy and bacterial motility analysis. Overall, visible light irradiation on coated solid surfaces mediated by proanthocyanidin showed no cytotoxicity and inactivated clinically important pathogens through the generation of reactive oxygen species, inhibiting bacterial initial adhesion. The developed coating is a promising alternative for a wide range of applications related to surface disinfection and food biopreservation.

Mitigation of viruses of concern and bacteriophage surrogates via common unit processes for water reuse: A meta-analysis

Water reuse is a growing global reality. In regulating water reuse, viruses have come to the fore as key pathogens due to high shedding rates, low infectious doses, and resilience to traditional wastewater treatments. To demonstrate the high log reductions required by emerging water reuse regulations, cost and practicality necessitate surrogates for viruses for use as challenge organisms in unit process evaluation and monitoring. Bacteriophage surrogates that are mitigated to the same or lesser extent than viruses of concern are routinely used for individual unit process testing. However, the behavior of these surrogates over a multi-barrier treatment train typical of water reuse has not been well-established. Toward this aim, we performed a meta-analysis of log reductions of common bacteriophage surrogates for five treatment processes typical of water reuse treatment trains: advanced oxidation processes, chlorination, membrane filtration, ozonation, and ultraviolet (UV) disinfection. Robust linear regression was applied to identify a range of doses consistent with a given log reduction of bacteriophages and viruses of concern for each treatment process. The results were used to determine relative conservatism of surrogates. We found that no one bacteriophage was a representative or conservative surrogate for viruses of concern across all multi-barrier treatments (encompassing multiple mechanisms of virus mitigation). Rather, a suite of bacteriophage surrogates provides both a representative range of inactivation and information about the effectiveness of individual processes within a treatment train. Based on the abundance of available data and diversity of virus treatability using these five key water reuse treatment processes, bacteriophages MS2, phiX174, and Qbeta were recommended as a core suite of surrogates for virus challenge testing.

Antimicrobial activity of silver-copper coating against aerosols containing surrogate respiratory viruses and bacteria

The transmission of bacteria and respiratory viruses through expelled saliva microdroplets and aerosols is a significant concern for healthcare workers, further highlighted during the SARS-CoV-2 pandemic. To address this issue, the development of nanomaterials with antimicrobial properties for use as nanolayers in respiratory protection equipment, such as facemasks or respirators, has emerged as a potential solution. In this study, a silver and copper nanolayer called SakCu® was deposited on one side of a spun-bond polypropylene fabric using the magnetron sputtering technique. The antibacterial and antiviral activity of the AgCu nanolayer was evaluated against droplets falling on the material and aerosols passing through it. The effectiveness of the nanolayer was assessed by measuring viral loads of the enveloped virus SARS-CoV-2 and viability assays using respiratory surrogate viruses, including PaMx54, PaMx60, PaMx61 (ssRNA, Leviviridae), and PhiX174 (ssDNA, Microviridae) as representatives of non-enveloped viruses. Colony forming unit (CFU) determination was employed to evaluate the survival of aerobic and anaerobic bacteria. The results demonstrated a nearly exponential reduction in SARS-CoV-2 viral load, achieving complete viral load reduction after 24 hours of contact incubation with the AgCu nanolayer. Viability assays with the surrogate viruses showed a significant reduction in viral replication between 2-4 hours after contact. The simulated viral filtration system demonstrated inhibition of viral replication ranging from 39% to 64%. The viability assays with PhiX174 exhibited a 2-log reduction in viral replication after 24 hours of contact and a 16.31% inhibition in viral filtration assays. Bacterial growth inhibition varied depending on the species, with reductions ranging from 70% to 92% for aerobic bacteria and over 90% for anaerobic strains. In conclusion, the AgCu nanolayer displayed high bactericidal and antiviral activity in contact and aerosol conditions. Therefore, it holds the potential for incorporation into personal protective equipment to effectively reduce and prevent the transmission of aerosol-borne pathogenic bacteria and respiratory viruses.

Inactivation characteristics of a 280 nm Deep-UV irradiation dose on aerosolized SARS-CoV-2

A non-filter virus inactivation unit was developed that can control the irradiation dose of aerosolized viruses by controlling the lighting pattern of a 280 nm deep-UV (DUV)-LED and the air flowrate. In this study, the inactivation properties of aerosolized SARS-CoV-2 were quantitatively evaluated by controlling the irradiation dose to the virus inside the inactivation unit. The RNA concentration of SARS-CoV-2 remained constant when the total irradiation dose of DUV irradiation to the virus exceeded 16.5 mJ/cm2. This observation suggests that RNA damage may occur in regions below the detection threshold of RT-qPCR assay. However, when the total irradiation dose was less than 16.5 mJ/cm2, the RNA concentration monotonically increased with a decreasing LED irradiation dose. However, the nucleocapsid protein concentration of SARS-CoV-2 was not predominantly dependent on the LED irradiation dose. The plaque assay showed that 99.16% of the virus was inactivated at 8.1 mJ/cm2 of irradiation, and no virus was detected at 12.2 mJ/cm2 of irradiation, resulting in a 99.89% virus inactivation rate. Thus, an irradiation dose of 23% of the maximal irradiation capacity of the virus inactivation unit can activate more than 99% of SARS-CoV-2. These findings are expected to enhance versatility in various applications. The downsizing achieved in our study renders the technology apt for installation in narrow spaces, while the enhanced flowrates establish its viability for implementation in larger facilities.

A review on led technology in water photodisinfection

The increase in efficiency achieved by UV LED devices has led to a compelling increase in research reports on UV LED water treatment for consumption in the past few years. This paper presents an in-depth review based on recent studies on the suitability and performance of UV LED-driven processes for water disinfection. The effect of different UV wavelengths and their combinations was analysed for the inactivation of various microorganisms and the inhibition of repair mechanisms. Whereas 265 nm UVC LED present a higher DNA damaging potential, 280 nm radiation is reported to repress photoreactivation and dark repair. No synergistic effects have been proved to exist when coupling UVB + UVC whereas sequential UVA-UVC radiation seemed to enhance inactivation. Benefits of pulsed over continuous radiation in terms of germicidal effects and energy consumption were also analysed, but with inconclusive results. However, pulsed radiation may be promising for improving thermal management. As a challenge, the use of UV LED sources introduces significant inhomogeneities in the light distribution, pushing for the development of adequate simulation methods to ensure that the minimum target dose required for the target microbes is achieved. Concerning energy consumption, selecting the optimal wavelength of the UV LED needs a compromise between the quantum efficiency of the process and the electricity-to-photon conversion. The expected development of the UV LED industry in the next few years points to UVC LED as a promising technology for water disinfection at a large scale that could be competitive in the market in the near future.

Microbial inactivation kinetics of UV LEDs and effect of operating conditions: A methodological critical analysis

Tiny ultraviolet (UV) light-emitting diodes (LED)s that are replacing the conventional energy-intensive mercury UV lamps have gained interest since the early 2000's because of their promising advantages. In the context of microbial inactivation (MI) of waterborne microbes, disinfection kinetics of those LEDs exhibited variations among studies, in terms of varying the UV wavelength, the exposure time, power, and dose (UV fluence) as well as other operational conditions. While reported results may appear contradictory when examined separately, they probably are not when analyzed collectively. As such, in this study, we carry out a quantitative collective regression analysis of the reported data to shed light on the kinetics of MI by the emerging UV LEDs technology alongside the effects of varying operational conditions. The main goal is to identify dose response requirements for UV LEDs and to compare them to traditional UV lamps in addition to ascertaining optimal settings that could help in achieving the optimal inactivation outcome for comparable UV doses. The analysis showed that kinetically, UV LEDs are as effective as conventional mercury lamps for water disinfection, and at times more effective, especially for UV resistant microbes. We defined the maximal efficiency at two wavelengths, 260-265 nm and 280 nm, among a wide range of available LED wavelengths. We also defined the UV fluence per log inactivation of tested microbes. At the operational level, we identified existing gaps and developed a framework for a comprehensive analysis program for future needs.

How to Tackle Bacteriophages: The Review of Approaches with Mechanistic Insight

Bacteriophage-based applications have a renaissance today, increasingly marking their use in industry, medicine, food processing, biotechnology, and more. However, phages are considered resistant to various harsh environmental conditions; besides, they are characterized by high intra-group variability. Phage-related contaminations may therefore pose new challenges in the future due to the wider use of phages in industry and health care. Therefore, in this review, we summarize the current knowledge of bacteriophage disinfection methods, as well as highlight new technologies and approaches. We discuss the need for systematic solutions to improve bacteriophage control, taking into account their structural and environmental diversity.

Ultrafast-UV laser integrating cavity device for inactivation of SARS-CoV-2 and other viruses

Ultraviolet (UV) irradiation-based methods used for viral inactivation have provided an important avenue targeting severe acute respiratory-syndrome coronavirus-2 (SARS-CoV-2) virus. A major problem with state-of-the-art UV inactivation technology is that it is based on UV lamps, which have limited efficiency, require high power, large doses, and long irradiation times. These drawbacks limit the use of UV lamps in air filtering systems and other applications. To address these limitations, herein we report on the fabrication of a device comprising a pulsed nanosecond 266 nm UV laser coupled to an integrating cavity (LIC) composed of a UV reflective material, polytetrafluoroethylene. Previous UV lamp inactivation cavities were based on polished walls with specular reflections, but the diffuse reflective UV ICs were not thoroughly explored for virus inactivation. Our results show that LIC device can inactivate several respiratory viruses including SARS-CoV-2, at ~ 1 ms effective irradiation time, with > 2 orders of magnitude higher efficiency compared to UV lamps. The demonstrated 3 orders of magnitude cavity enhancement relative to direct exposure is crucial for the development of efficient real-time UV air and water purification systems. To the best of our knowledge this is the first demonstration of LIC application for broad viral inactivation with high efficiency.

Evaluation of Virucidal Efficacy of Human Norovirus Using Combined Sprayed Slightly Acidic Electrolyzed Water and Ultraviolet C-Light-Emitting Diode Irradiation Treatment Based on Optimized Capture Assay for Quantitative RT-qPCR

Slightly acidic electrolyzed water (SAEW), an effective non-thermal virucidal treatment, is used widely to prevent infectious viral cross-contamination. Surface disinfection technologies using ultraviolet C-light-emitting diode (UVC-LED) irradiation have recently attracted considerable attention. The SAEW sprayer technique is an efficient approach to preventing the spread of infectious viral pathogens in the public healthcare sector. Therefore, we investigated a small-scale system comprising sprayed SAEW disinfection combined with UVC-LED irradiation to inactivate the human norovirus (HuNoV) in the environment. A stainless-steel surface was inoculated with a HuNoV genogroup II genotype 4 (GII.4) to achieve maximum reduction values of 3.21 log10 genomic copies. For optimal disinfection conditions, the response surface methodology based on the Box–Behnken design revealed that the specific treatment conditions for inactivation of HuNoV GII.4 were an SAEW droplet volume of 180 μL, 30 ppm available chlorine concentration of SAEW, and a UVC-LED exposure dose of 2 mJ/cm². The results indicate that the combined disinfection treatment could efficiently prevent the spread of HuNoVs in environment. Furthermore, the quadratic polynomial equations of the 3-D response surface can be employed to predict the effects of combined disinfection treatment on HuNoV contamination on environmental surfaces. Therefore, sprayed SAEW disinfection combined with UVC-LED irradiation proposed in this study may offer insights for designing optimal control strategies and techniques to prevent the transmission of infectious diseases, particularly HuNoV.

A Comprehensive Analysis of the UVC LEDs' Applications and Decontamination Capability

The application of light-emitting diodes (LEDs) has been gaining popularity over the last decades. LEDs have advantages compared to traditional light sources in terms of lifecycle, robustness, compactness, flexibility, and the absence of non-hazardous material. Combining these advantages with the possibility of emitting Ultraviolet C (UVC) makes LEDs serious candidates for light sources in decontamination systems. Nevertheless, it is unclear if they present better decontamination effectiveness than traditional mercury vapor lamps. Hence, this research uses a systematic literature review (SLR) to enlighten three aspects: (1) UVC LEDs' application according to the field, (2) UVC LEDs' application in terms of different biological indicators, and (3) the decontamination effectiveness of UVC LEDs in comparison to conventional lamps. UVC LEDs have spread across multiple areas, ranging from health applications to wastewater or food decontamination. The UVC LEDs' decontamination effectiveness is as good as mercury vapor lamps. In some cases, LEDs even provide better results than conventional mercury vapor lamps. However, the increase in the targets' complexity (e.g., multilayers or thicker individual layers) may reduce the UVC decontamination efficacy. Therefore, UVC LEDs still require considerable optimization. These findings are stimulating for developing industrial or final users' applications.

Stormwater treatment for reuse: Current practice and future development - A review

Stormwater harvesting is an effective measure to mitigate flooding risk and pollutant migration in our urban environment with the continuously increasing impermeable faction. Treatment of harvested stormwater also provides the fit-for-purpose water sources as an alternative to potable water supply ensuring the reliability and sustainability of the water management in the living complex. In order to provide the water management decision-maker with a broad range of related technology database and to facilitate the implementation of stormwater harvesting in the future, a comprehensive review was undertaken to understand the corresponding treatment performance, the applicable circumstances of current stormwater treatment and harvesting technologies. Technologies with promising potential for stormwater treatment were also reviewed to investigate the feasibility of being used in an integrated process. The raw stormwater quality and the required quality for different levels of stormwater reuses (irrigation, recreational, and potable) were reviewed and compared. The required level of treatment is defined for different 'fit-for-purpose' uses of harvested stormwater. Stormwater biofilter and constructed wetland as the two most advanced and widely used stormwater harvesting and treatment technologies, their main functionality, treatment performance and adequate scale of the application were reviewed based on published peer-reviewed articles and case studies. Excessive microbial effluent that exists in stormwater treated using these two technologies has restricted the stormwater reuse in most cases. Water disinfection technologies developed for wastewater and surface water treatment but with high potential to be used for stormwater treatment have been reviewed. Their feasibility and limitation for stormwater treatment are presented with respect to different levels of fit-for-purpose reuses. Implications for future implementation of stormwater treatment are made on proposing treatment trains that are suitable for different fit-for-purpose stormwater reuses.

UVC-based photoinactivation as an efficient tool to control the transmission of coronaviruses

The ongoing COVID-19 pandemic made us re-realize the importance of environmental disinfection and sanitation in indoor areas, hospitals, and clinical rooms. UVC irradiation of high energy and short wavelengths, especially in the 200-290-nm range possesses the great potential for germicidal disinfection. These properties of UVC allow to damage or destruct the nucleic acids (DNA/RNA) in diverse microbes (e.g., bacteria, fungi, and viruses). UVC light can hence be used as a promising tool for prevention and control of their infection or transmission. The present review offers insights into the historical perspective, mode of action, and recent advancements in the application of UVC-based antiviral therapy against coronaviruses (including SARS CoV-2). Moreover, the application of UVC lights in the sanitization of healthcare units, public places, medical instruments, respirators, and personal protective equipment (PPE) is also discussed. This article, therefore, is expected to deliver a new path for the developments of UVC-based viricidal approach.

Surface chemistry-dependent antiviral activity of silver nanoparticles

The toxicity towards viruses of silver nanoparticles (AgNPs) has been reported to be dependent on several factors such as particle concentration, size, and shape. Although these factors may indeed contribute to the toxicity of AgNPs, the results presented in this work demonstrate that surface chemistry and especially surface charge is a crucial factor governing their antiviral activity. Here, this work investigated the influence of capping agents representing various surface charges ranging from negative to positive. These AgNPs were capped with citrate, polyethylene glycol (PEG), polyvinylpyrrolidone (PVP) mercaptoacetic acid (MAA) and (branched polyethyleneimine (BPEI). We show that AgNPs exhibited surface charge-dependent toxicity towards MS2 bacteriophages. Among the capping agents under investigation, BPEI capped AgNPs (Ag/BPEI) exhibited the highest reduction of MS2 resulting in ≥6 log₁₀-units reductions, followed by 4-5 log₁₀-units reductions with PVP and PEG capping's and 3-4 log₁₀-units with MAA and citrate cappings. Bare nanoparticles reported a mere 1-2 log₁₀-units reduction. Electrostatic interaction between the positively charged BPEI-coating and the negatively charged virus surface played a significant role in bringing the MS2 closer to toxic silver ions (Ag⁺). Further results obtained from TEM showed that Ag/BPEI nanoparticles could directly damage the structure of the MS2 bacteriophages. AgNPs and cationic capping agents' observed synergy can lead to much lower and much more efficient dosing of AgNPs for antiviral applications.

Efficacy of light-emitting diodes emitting 395, 405, 415, and 425 nm blue light for bacterial inactivation and the microbicidal mechanism

We investigated the bactericidal effects against Escherichia coli O157:H7 of light-emitting diodes (LEDs) emitting blue light of four different peak wavelengths ranging from 395 to 425 nm in water. Furthermore, we investigated inactivation in the presence of reactive oxygen species (ROS) scavengers to elucidate the contribution of bacterial inactivation. An aluminum chamber was constructed and coated in carbon to block exterior light, and a single blue light LED with a rear heat sink was attached to the chamber lid. Effective inactivation of the pathogen was observed for all blue light LED irradiation at 305, 405, 415, and 425 nm. The log-linear with shoulder and tail model and log-linear model described the survival of the bacteria after blue light LED treatments. Not just the effects of ROS but also photophysical effects were shown with the addition of mannitol, a ROS scavenger. The integrity of the cell membrane was damaged regardless of the presence of ROS, which indicates that photophysical effects were sufficient to induce damage to the cell membrane. In addition, activity of succinate-coenzyme Q reductase, which participates in respiratory metabolism to generate energy, decreased in the absence of ROS and decreased further in the presence of ROS.

Survival of the enveloped bacteriophage Phi6 (a surrogate for SARS-CoV-2) in evaporated saliva microdroplets deposited on glass surfaces

Survival of respiratory viral pathogens in expelled saliva microdroplets is central to their transmission, yet the factors that determine survival in such microdroplets are not well understood. Here we combine microscopy imaging with virus viability assays to study survival of three bacteriophages suggested as good models for respiratory pathogens: the enveloped Phi6 (a surrogate for SARS-CoV-2), and the non-enveloped PhiX174 and MS2. We measured virus viability in human saliva microdroplets, SM buffer, and water following deposition on glass surfaces at various relative humidities (RH). Saliva and water microdroplets dried out rapidly, within minutes, at all tested RH levels (23%, 43%, 57%, and 78%), while SM microdroplets remained hydrated at RH ≥ 57%. Generally, the survival of all three viruses in dry saliva microdroplets was significantly greater than those in SM buffer and water under all RH (except PhiX174 in water under 57% RH survived the best among 3 media). Thus, atmosphere RH and microdroplet hydration state are not sufficient to explain virus survival, indicating that the virus-suspended medium, and association with saliva components in particular, likely play a role in virus survival. Uncovering the exact properties and components that make saliva a favorable environment for the survival of viruses, in particular enveloped ones like Phi6, is thus of great importance for reducing transmission of viral respiratory pathogens including SARS-CoV-2.

Survival of the enveloped bacteriophage Phi6 (a surrogate for SARS-CoV-2) in evaporated saliva microdroplets deposited on glass surfaces

Survival of respiratory viral pathogens in expelled saliva microdroplets is central to their transmission, yet the factors that determine survival in such microdroplets are not well understood. Here we combine microscopy imaging with virus viability assays to study survival of three bacteriophages suggested as good models for respiratory pathogens: the enveloped Phi6 (a surrogate for SARS-CoV-2), and the non-enveloped PhiX174 and MS2. We measured virus viability in human saliva microdroplets, SM buffer, and water following deposition on glass surfaces at various relative humidities (RH). Saliva and water microdroplets dried out rapidly, within minutes, at all tested RH levels (23%, 43%, 57%, and 78%), while SM microdroplets remained hydrated at RH ≥ 57%. Generally, the survival of all three viruses in dry saliva microdroplets was significantly greater than those in SM buffer and water under all RH (except PhiX174 in water under 57% RH survived the best among 3 media). Thus, atmosphere RH and microdroplet hydration state are not sufficient to explain virus survival, indicating that the virus-suspended medium, and association with saliva components in particular, likely play a role in virus survival. Uncovering the exact properties and components that make saliva a favorable environment for the survival of viruses, in particular enveloped ones like Phi6, is thus of great importance for reducing transmission of viral respiratory pathogens including SARS-CoV-2.

Control Measures for SARS-CoV-2: A Review on Light-Based Inactivation of Single-Stranded RNA Viruses

SARS-CoV-2 is a single-stranded RNA virus classified in the family Coronaviridae. In this review, we summarize the literature on light-based (UV, blue, and red lights) sanitization methods for the inactivation of ssRNA viruses in different matrixes (air, liquid, and solid). The rate of inactivation of ssRNA viruses in liquid was higher than in air, whereas inactivation on solid surfaces varied with the type of surface. The efficacy of light-based inactivation was reduced by the presence of absorptive materials. Several technologies can be used to deliver light, including mercury lamp (conventional UV), excimer lamp (UV), pulsed-light, and light-emitting diode (LED). Pulsed-light technologies could inactivate viruses more quickly than conventional UV-C lamps. Large-scale use of germicidal LED is dependent on future improvements in their energy efficiency. Blue light possesses virucidal potential in the presence of exogenous photosensitizers, although femtosecond laser (ultrashort pulses) can be used to circumvent the need for photosensitizers. Red light can be combined with methylene blue for application in medical settings, especially for sanitization of blood products. Future modelling studies are required to establish clearer parameters for assessing susceptibility of viruses to light-based inactivation. There is considerable scope for improvement in the current germicidal light-based technologies and practices.

A novel upper-room UVC-LED irradiation system for disinfection of indoor bioaerosols under different operating and airflow conditions

The potential of inactivating indoor bacteria aerosols using a novel rotating ultraviolet-C (UV-C) light-emitting-diode (LED) system was investigated. The system was installed in the upper level of a full scale chamber and its effectiveness against aerosolized E. coli, S. marcescens, and S. epidermidis under the well-mixed with stationary UV-LED scenario was initially tested. The estimated susceptibility values were 1.068, 1.148, and 0.156 m²/J for E. coli, S. marcescens, and S. epidermidis, respectively. Three additional scenarios of experiments were conducted, in which E. coli was aerosolized into the test chamber and then allowed to decay under (i) poorly-mixed condition with stationary system, (ii) well-mixed with rotating system, and (iii) poorly-mixed conditions with rotating system. Our results showed no significant difference between the performance of stationary and rotating UR-UVGI-LED systems under a well-mixed condition. While the performance of the stationary UR-UVGI-LED system under a poorly-mixed condition decreased by 52.90-79.38 % compared to a well-mixed condition, rotating the UR-UVGI-LED system under a poorly-mixed condition, compared to the stationary system, enhanced its performance by 22.36-49.86 %. Thus, our proposed rotating irradiation offers great potential for application in environments where bioaerosols are unevenly distributed in a built environment.

Irradiation by a Combination of Different Peak-Wavelength Ultraviolet-Light Emitting Diodes Enhances the Inactivation of Influenza A Viruses

Influenza A viruses (IAVs) pose a serious global threat to humans and their livestock. This study aimed to determine the ideal irradiation by ultraviolet-light emitting diodes (UV-LEDs) for IAV disinfection. We irradiated the IAV H1N1 subtype with 4.8 mJ/cm² UV using eight UV-LEDs [peak wavelengths (WL) = 365, 310, 300, 290, 280, 270, and 260 nm)] or a mercury low pressure (LP)-UV lamp (Peak WL = 254 nm). Inactivation was evaluated by the infection ratio of Madin–Darby canine kidney (MDCK) cells or chicken embryonated eggs. Irradiation by the 260 nm UV-LED showed the highest inactivation among all treatments. Because the irradiation-induced inactivation effects strongly correlated with damage to viral RNA, we calculated the correlation coefficient (R_AE) between the irradiant spectrum and absorption of viral RNA. The R_AE scores strongly correlated with the inactivation by the UV-LEDs and LP-UV lamp. To increase the R_AE score, we combined three different peak WL UV-LEDs (hybrid UV-LED). The hybrid UV-LED (R_AE = 86.3) significantly inactivated both H1N1 and H6N2 subtypes to a greater extent than 260 nm (R_AE = 68.6) or 270 nm (R_AE = 42.2) UV-LEDs. The R_AE score is an important factor for increasing the virucidal effects of UV-LED irradiation.

UV Photolysis of Mono- and Dichloramine Using UV-LEDs as Radiation Sources: Photodecay Rates and Radical Concentrations

UV-LEDs with four characteristic wavelengths (255, 265, 285, and 300 nm) were used to investigate the wavelength-dependence of the photolysis of two inorganic chloramines (NH₂Cl and NHCl₂) and their subsequent radical formation. The fluence-based photodecay rates of NH₂Cl decreased with increasing wavelength from 255 to 300 nm, while NHCl₂ photodecay rates exhibited the opposite wavelength-dependence. The fluence-based photodecay rate of NH₂Cl was comparable to that of NHCl₂ at 255 nm, but was lower than NHCl₂ at other tested wavelengths. The wavelength-dependence was more influenced by the molar absorption coefficient than the apparent/innate quantum yield and the lower photosensitivity was mainly attributed to the higher bond (N-Cl) dissociation energy (BDE) of NH₂Cl than NHCl₂. The steady-state concentrations of HO^• and reactive chlorine species (e.g., Cl₂^•-, ClO^•, and Cl^•) that were generated from the photolysis of NH₂Cl and NHCl₂ at different wavelengths were determined experimentally and compared with the simulated results by a kinetic model. UV photolysis of NHCl₂ at 265, 285, and 300 nm generated higher concentrations of radicals (e.g., HO^•, ClO^•, Cl^•, and Cl₂^-•) than NH₂Cl, while UV photolysis of NH₂Cl at 255 nm generated higher concentrations of HO^•, ClO^•, and Cl^• but not Cl₂^-• than NHCl₂. The findings of this study provide fundamental information to be used in selecting specific wavelengths of UV radiation for enhancing/optimizing NH₂Cl/NHCl₂ photodecay in swimming pools and radical generation for micropollutant abatement in drinking water treatment or potable water reuse.

Inactivation Kinetics and Membrane Potential of Pathogens in Soybean Curd Subjected to Pulsed Ohmic Heating Depending on Applied Voltage and Duty Ratio

The aim of this research was to investigate the efficacy of the duty ratio and applied voltage in the inactivation of pathogens in soybean curd by pulsed ohmic heating (POH). The heating rate of soybean curd increased rapidly as the applied voltage increased, although the duty ratio did not affect the temperature profile. We supported this result by verifying that electrical conductivity increased with the applied voltage. Escherichia coli O157:H7, Salmonella enterica serovar Typhimurium, and Listeria monocytogenes in soybean curd were significantly (P < 0.05) inactivated by more than 1 log unit at 80 Vrms (root mean square voltage). To elucidate the mechanism underlying these results, the membrane potential of the pathogens was examined using DiBAC4(3) [bis-(1,3-dibutylbarbituric acid)trimethine oxonol] on the basis of a previous study showing that the electric field generated by ohmic heating affected the membrane potential of cells. The values of DiBAC4(3) accumulation increased under increasing applied voltage, and they were significantly (P < 0.05) higher at 80 Vrms, while the duty ratio had no effect. In addition, morphological analysis via transmission electron microscopy showed that electroporation and expulsion of intracellular materials were predominant at 80 Vrms Moreover, electrode corrosion was overcome by the POH technique, and the textural and color properties of soybean curd were preserved. These results substantiate the idea that the applied voltage has a profound effect on the microbial inactivation of POH as a consequence of not only the thermal effect, but also the nonthermal effect, of the electric field, whereas the duty ratio does not have such an effect.IMPORTANCE High-water-activity food products, such as soybean curd, are vulnerable to microbial contamination, which causes fatal foodborne diseases and food spoilage. Inactivating microorganisms inside food is difficult because the transfer of thermal energy is slower inside than it is outside the food. POH is an adequate sterilization technique because of its rapid and uniform heating without causing electrode corrosion. To elucidate the electrical factors associated with POH performance in the inactivation of pathogens, the effects of the applied voltage and duty ratio on POH were investigated. In this study, we verified that a high applied voltage (80 Vrms) at a duty ratio of 0.1 caused thermal and nonthermal effects on pathogens that led to an approximately 4-log-unit reduction in a significantly short time. Therefore, the results of this research corroborate database predictions of the inactivation efficiency of POH based on pathogen control strategy modeling.

Virus inactivation in groundwater in a postglacial lava field in arctic climate

Outbreaks of viral gastroenteritis are often connected to contaminated drinking water. The assessment of the water quality relies on the cultivation of indicator bacteria, and little is known of the fate of viruses in groundwater, especially in arctic regions. In Iceland, the groundwater temperature is between 3 and 6°C. The aim of this study was to determine virus inactivation at low temperature in a groundwater microcosm and in a borehole in a postglacial lava field. Two phage species that are commonly used as surrogates for norovirus were used, MS2 and PhiX174. Dialysis bags were used for the samples, and a device was constructed to hold many samples at a time and protect the samples in the borehole. No significant decrease of infective PhiX174 phages in the borehole or of the MS2 phages in the microcosm was observed. A slightly significant decrease of PhiX174 in the microcosm was noticed, with one log reduction time of 476 days. On the other hand, a significant reduction in MS2 was found in the field test, where the time needed for 90% reduction was 12·5 days. The results showed that an infective virus can exist in groundwater for months or years in arctic regions and a great difference may exist between results from microcosm and field tests. SIGNIFICANCE AND IMPACT OF THE STUDY: This study reveals that arctic regions are highly sensitive to virus contamination as an infective virus may exist in groundwater for years at low temperature. The results also show that the virus inactivation observed in field tests may differ considerably from the inactivation observed in laboratory microcosms. The results emphasize the importance of large protection zones around drinking water intakes as well as good wastewater treatment so that the likelihood of faecal contamination of groundwater is reduced.

Application of Ultraviolet Light-Emitting Diodes (UV-LED) to Full-Scale Drinking-Water Disinfection

Ultraviolet light-emitting diodes (UV-LEDs) have recently emerged as a viable technology for water disinfection. However, the performance of the technology in full-scale drinking-water treatment systems remains poorly characterised. Furthermore, current UV disinfection standards and protocols have been developed specifically for conventional mercury UV systems and so do not necessarily provide an accurate indication of UV-LED disinfection performance. Hence, this study aimed to test the hypothesis that a full-scale UV-LED reactor can match the Cryptosporidium inactivation efficiency of conventional mercury UV reactors. Male-specific bacteriophage (MS2) was used as the Cryptosporidium spp. surrogate microorganism. The time-based inactivation efficiency of the full-scale reactor was firstly compared to that of a bench-scale (batch-type) UV-LED reactor. This was then related to mercury UV reactors by comparing the fluence-based efficiency of the bench-scale reactor to the USEPA 90% prediction interval range of expected MS2 inactivation using mercury UV lamps. The results showed that the full-scale UV-LED reactor was at least as effective as conventional mercury UV reactors at the water-quality and drive-current conditions considered. Nevertheless, comparisons between the bench- and full-scale UV-LED reactors indicated that improvements in the hydraulic flow profile and power output of the full-scale reactor could help to further improve the efficiency of UV-LED reactors for municipal drinking water disinfection. This represents the world’s first full-scale UV-LED reactor that can be applied at municipal water treatment works for disinfection of pathogenic microorganisms from drinking water.

Thinking Outside the Treatment Plant: UV for Water Distribution System Disinfection

This work critically evaluates the current paradigm of water distribution system management and juxtaposes that with the potential benefits of employing UV irradiation, which we hope will catalyze a judicial re-evaluation of the current practices in water distribution system management and spur critical research and a new way of thinking about secondary disinfection across the extent of distribution systems. Given the recent advances in UV technology and the efficacy of UV disinfection against all pathogen classes, we now see UV applications for disinfection in many aspects of consumers lives: in water coolers, dishwashers, coffee makers, and disinfection of personal items like gym bags, water bottles, and toothbrushes. Public and regulatory concern over water quality and pathogens, especially the recent interest in building plumbing, calls out for new approaches to disinfection and distribution system management. We envision a new model for secondary disinfection in water distribution systems utilizing emerging germicidal UV LED-based disinfection. UV irradiation in water treatment can achieve high levels of disinfection of all pathogens and minimize or eliminate the formation of regulated disinfection byproducts. So why is UV not considered as a secondary disinfectant for distribution systems? In this Account, we lay out the logic as to the benefits and practicality of adding distributed UV treatment to assist in protection of distribution systems and protect water quality for human exposure. The possible locations of UV irradiation in distribution systems are envisioned, potentially including UV booster stations along the distribution network, UV in storage tanks or their inlet/outlets, LEDs distributed along pipe walls, small point of use/entry treatment systems for buildings/homes/taps, or submersible swimming or rolling UV LED drones to reach problem pipes and provide a "shock" treatment or provide sterilization after main breaks or repairs. The benefits of UV applications in water also include high effectiveness against chlorine-resistant protozoa, no added disinfection byproducts, and compatibility of adding of UV to existing secondary disinfection strategies for enhanced protection. Potential challenges and research needs are described, such as use of UV-compatible pipe materials, implementation of sensors to monitor distributed LEDs, management of waste heat from the rear surface of the LED, and understanding the potential for regrowth of opportunistic microorganisms. Another notable challenge is the relatively stagnant regulatory environment in some countries to develop frameworks for evaluation and acceptance of UV technology in distribution systems that require a chemical secondary disinfectant. Rapid advances in UV LED research has propelled the growth of this field, but needs still remain, including understanding behavior of biofilms in pipes under UV irradiation, including any beneficial effects that may be lost, the potential for fouling of LED emission surfaces and monitoring points, and provision of a distributed power network to run the LEDs. Regulators may want specific monitoring approaches and advances in real-time monitoring of microbial viability, and engineers may need to develop new approaches to overall management.

Evaluation survey of microbial disinfection methods in UV-LED water treatment systems

Ultraviolet (UV) disinfection is an early discovered technology that is currently and widely used for water treatment and food hygiene treatment. A newly emerging technology of UV disinfection, that is, UV light-emitting diodes (UV-LEDs), has aroused considerable research attention. UV-LEDs feature numerous advantages compared with traditional UV mercury vapor lamps and are expected to replace traditional UV lamps. Researchers currently perform studies to obtain data and develop methods for UV-LED water treatment systems. This article analyzes the latest research status and discusses the types of inactivation factors, such as the wavelength selectivity of UV light source, control of UV dose, effect of inactivation rate constant (K) (cm²/mJ), working mode of water sample, external auxiliary system, and UV sensitivity of pathogenic bacteria in water. The wavelengths of approximately 260 and 280 nm normally feature strong inactivation characteristics. When compared with the approximately 260 nm wavelength chip, the around 280 nm wavelength chip proves to be a better choice as its higher wavelength light power can result in faster disinfection capacity of bacteria. UV dose can also be used as the reference value for disinfection of drinking water, whereas the inactivation rate constant (K) (cm²/mJ) varies with different microorganism internal structures. Changing the working mode or adding an auxiliary system can also enhance the inactivation effect in water treatment system settings. In addition, we can compare the inactivation capacities of several pathogens as follows: ΦX174 > Escherichia coli > T type bacteriophage >Bacillus subtilis > MS2 or Qβ > human adenovirus. The in-depth investigation and discussion of inactivation factors and the mechanism of action in UV-LEDs water treatment systems will establish a more efficient UV-LED disinfection method in the future, provide a guiding direction, and promote the standardization and normalization of pathogen inactivation mechanism in UV-LED water treatment systems.

Irradiation by ultraviolet light-emitting diodes inactivates influenza a viruses by inhibiting replication and transcription of viral RNA in host cells

Influenza A viruses (IAVs) pose a serious global threat to humans and their livestock, especially poultry and pigs. This study aimed to investigate how to inactivate IAVs by using different ultraviolet-light-emitting diodes (UV-LEDs). We developed sterilization equipment with light-emitting diodes (LEDs) those peak wavelengths were 365 nm (UVA-LED), 310 nm (UVB-LED), and 280 nm (UVC-LED). These UV-LED irradiations decreased dose fluence-dependent plaque-forming units of IAV H1N1 subtype (A/Puerto Rico/8/1934) infected Madin-Darby canine kidney (MDCK) cells, but the inactivation efficiency of UVA-LED was significantly lower than UVB- and UVC-LED. UV-LED irradiations did not alter hemagglutination titer, but decreased accumulation of intracellular total viral RNA in infected MDCK cells was observed. Additionally, UV-LED irradiations suppressed the accumulation of intracellular mRNA (messenger RNA), vRNA (viral RNA), and cRNA (complementary RNA), as measured by strand-specific RT-PCR. These results suggest that UV-LEDs inhibit host cell replication and transcription of viral RNA. Both UVB- and UVC-LED irradiation decreased focus-forming unit (FFU) of H5N1 subtype (A/Crow/Kyoto/53/2004), a highly pathogenic avian IAV (HPAI), in infected MDCK cells, and the amount of FFU were lower than the H1N1 subtype. From these results, it appears that IAVs may have different sensitivity among the subtypes, and UVB- and UVC-LED may be suitable for HPAI virus inactivation.

Synergy of MS2 disinfection by sequential exposure to tailored UV wavelengths

The advantages of polychromatic ultraviolet (UV) light for viral disinfection can be optimized for disinfection using emerging tailored wavelength sources including KrCl excimer lamps and light emitting diodes (LEDs). Disinfection of the common viral surrogate MS2 bacteriophage was measured after exposure to these emerging sources and conventional low pressure (LP) mercury UV lamps in individual or sequential exposures. The first dose response for any virus (MS2) exposed to a KrCl excimer lamp is reported, showing the high efficiency of fluence-based disinfection because of increased viral susceptibility at the low wavelengths emitted by the excilamp. Sequential exposure dose responses indicated synergy from sequential exposures of LP and excimer lamps, which were competitive on an electrical basis at worst-and best-case scenarios of wall plug efficiency with current medium pressure (MP) disinfection. Best-case scenarios for electrical efficiency also showed all sequential exposures to be competitive with MP UV disinfection. Predictive models for sequential exposure dose responses were assessed to support the current feasibility of incorporating sequential UV exposures to optimize tailored wavelength viral disinfection.

Elevated Inactivation Efficacy of a Pulsed UVC Light-Emitting Diode System for Foodborne Pathogens on Selective Media and Food Surfaces

UVC light, a strong surface disinfection technology, is used worldwide to ensure not only environmental safety but also food safety. Several drawbacks associated with the use of mercury-containing UV lamps, especially human and environmental health risks, led to the Minamata Convention on Mercury, which prohibits the manufacture and import/export of products containing mercury. Therefore, light-emitting diode (LED)-based UVC irradiation, a new technology that is ecofriendly and represents an effective UV light source, has been researched recently. To date, however, there has been no report describing pulsed UVC-LED irradiation for improvement of inactivation of foodborne pathogens, although much research regarding conventional pulsed xenon lamps has been published. In this investigation, we evaluated the enhanced bactericidal effect of a pulsed UVC-LED system, compared to continuous irradiation, and optimum conditions for maximizing the effect were determined. Also, the differences in inactivation between pulsed and continuous UVC-LED irradiation were determined by inactivation mechanism analyses. The combination of 20-Hz frequency and 50% duty ratio for pulsed UVC-LED irradiation achieved 4- to 5-log-unit reductions of Escherichia coli O157:H7, Salmonella enterica serovar Typhimurium, and Listeria monocytogenes; this combination showed the greatest bactericidal effect among various treatment conditions using 2 or 5 mJ/cm² In mechanism assessments, membrane integrity (propidium iodide uptake) was not affected by UVC-LED treatment but membrane potential [bis-(1,3-dibutylbarbituric acid)trimethine oxonol [DiBAC₄(3)] accumulation] showed significantly different values when pulsed and continuous treatments were compared. Changes in membrane lipid peroxidation and respiratory enzyme activity were attributed to generation of more reactive oxygen species by pulsed UVC-LED irradiation.IMPORTANCE In 2013, the United Nations Environment Programme convened the Minamata Convention on Mercury, which prohibits trade in mercury-containing products in order to ensure human health. It will be effectuated in 2020; use of low-pressure mercury lamps will be discontinued and a new UV light source selected to replace the conventional technology. In this regard, UVC-LEDs have been developed and the fundamental inactivating effect has been researched. However, a pulsed UVC-LED system has not been studied, because of the difficulty of generating a UVC-LED pulse wave. An optical chopper system that physically divides the light with an adjustable blade, with personalized frequency and duty ratio settings, was introduced for generation of pulsed UVC-LED irradiation. This study elucidated the efficacy of a pulsed UVC-LED system and investigated its enhanced bactericidal effect in mechanism analyses.

UVC LED Irradiation Effectively Inactivates Aerosolized Viruses, Bacteria, and Fungi in a Chamber-Type Air Disinfection System

In this study, the possibility of inactivating viral, bacterial, and fungal aerosols in a chamber-type air disinfection system by using a UVC light-emitting-diode (LED) array was investigated and inactivation rate constants of each microorganism were calculated in fitting curves of surviving populations. UVC LED array treatment effectively inactivated viral infectivity, achieving 5-log reductions within 45 mJ/cm² for MS2, Qβ, and ϕX174 viruses. UVC LED array effectiveness in inactivating Escherichia coli O157:H7, Salmonella enterica serovar Typhimurium, Listeria monocytogenes, and Staphylococcus aureus aerosols achieved 2.5- to 4-log reductions within 1.5 to 4.6 mJ/cm² Also, 4-log reductions of Aspergillus flavus and Alternaria japonica were achieved at a dosage of 23 mJ/cm² using UVC LED array irradiation. The highest UV susceptibility, represented by the inactivation rate constant, was calculated for bacteria, followed by fungi and viruses. UVC LED, an innovative technology, can effectively inactivate microorganisms regardless of taxonomic classification and can sufficiently substitute for conventional mercury UV lamps.IMPORTANCE The United Nations Environment Programme (UNEP) convened the Minamata Convention on Mercury in 2013 to ban mercury-containing products in order to ensure human and environmental health. It will be effectuated in 2020 to discontinue use of low-pressure mercury lamps and new UV-emitting sources have to replace this conventional technology. However, the UV germicidal irradiation (UVGI) system still uses conventional UV lamps, and no research has been conducted for air disinfection using UVC LEDs. The research reported here investigated the inactivation effect of aerosolized microorganisms, including viruses, bacteria, and fungi, with an UVC LED module. The results can be utilized as a primary database to replace conventional UV lamps with UVC LEDs, a novel type of UV emitter. Implementation of UVC LED technology is truly expected to significantly reduce the extent of global mercury contamination, and this study provides important baseline data to help ensure a healthier environment and increased health for humanity.

Persistence of Norovirus GII Genome in Drinking Water and Wastewater at Different Temperatures

Human norovirus (NoV) causes waterborne outbreaks worldwide suggesting their ability to persist and survive for extended periods in the environment. The objective of this study was to determine the persistence of the NoV GII genome in drinking water and wastewater at three different temperatures (3 °C, 21 °C, and 36 °C). The persistence of two NoV GII inoculums (extracted from stool) and an indigenous NoV GII were studied. The samples were collected for up to one year from drinking water and for up to 140 days from wastewater. Molecular methods (RT-qPCR) were used to assess the decay of the NoV genome. Decay rate coefficients were determined from the fitted decay curves using log-linear and/or non-linear model equations. Results showed significant differences in the decay kinetics of NoV genome between the temperatures, matrices, and virus strains. The persistence of NoV was higher in drinking water compared to wastewater, and the cold temperature assisted persistence at both matrices. Differences between the persistence of NoV strains were also evident and, particularly, indigenous NoVs persisted better than spiked NoVs in wastewater. The decay constants obtained in this study can be utilized to assess the fate of the NoV genome in different water environments.